1. Field of the Invention
The present invention relates to vehicle safety devices and more specifically, to pneumatic tire height sensors, as utilized in low tire warning systems.
2. Description of the Prior Art
As outlined in the above-noted copending application there are generally two approaches to monitoring pneumatic vehicle tires and providing operator warning when a monitored tire is approaching a failure mode.
A historically conventional technique, for which a large body of prior art has evolved, is the monitoring of pressure within a pneumatic tire and comparing that internal pressure with a standard pressure or atmospheric pressure to determine when the tire pressure is below a predetermined value.
A more recently developed technique involves the monitoring of the road contact profile height of the pneumatic tire in order to sense low inflation pressure or overload of the tire. It is believed that the profile height monitoring technique is a more reliable reflection of tire condition, since the predicted wear life of a tire is based upon inflation pressure and load factors. A system that detects under-inflation and/or overload and produces a warning signal allows the vehicle operator to make appropriate adjustments in order to avoid excessive wear.
A self-contained tire height sensor is shown in U.S. Pat. No. 4,117,452, wherein a sensing probe is mounted onto the wheel of a pneumatic tire and is radially oriented so as to be actuated by the inner casing of the tire when the tire is under-inflated or overloaded and the sensor is between the wheel and ground. Upon compression of the probe, a piezoelectric generator is actuated and a signal is transmitted from an associated transmitter circuit to a receiver remotely located within the vehicle. The probe/piezoelectric generator/transmitter is formed as a unitary structure and is mounted within the inflation chamber defined by the wheel and tire. Any failure of the electronics in this prior art system, requires the removal of the tire from the wheel in order to change the module.
The present invention is intended to overcome the serviceability disadvantages of the profile height sensors described in the prior art.